In the art of internal transportation in factories, there are often used self-powered industrial material handling systems, which consist of a suspended monorail on which run powered trolleys powered through an electric distribution line arranged along the rail.
The trolleys usually have a drive wheel above the monorail and bucking rollers placed below it. Traction is thus assured by the adherence of the powered upper wheel on the monorail. This adherence is usually sufficient for movement on the level or along slight rises due to the weight of the trolley itself including the load carried by it and pulling down on the drive wheel.
For sloping sections with relatively steep slopes there have been proposed lower bucking rollers equipped with a pressure means such as a spring-loaded system that pushes the rollers toward the rail so as to increase the adherence or traction of the drive wheel on the rail as described for example in Italian patent No. 202,807 in the name of FATA European Group.
The use of bucking rollers, however, causes problems due to variations in the compression of the pressure means in the curved and radiused sections between sections with different slopes. The bucking rollers are usually two in number and are positioned along the chords of the curved sections. Hence if they are inside a curve they tend to draw away the powered wheel and if they are on the outside they draw near it. Consequently, in the former case, the springs are more compressed and in the latter case they are less compressed slope variations.
To prevent these compression differences from causing excessive and deleterious variations in traction, there have been proposed various solutions which, however, suffer from several drawbacks.
For example, there have been proposed thrust springs with a length much greater than the extension caused by variations in the rail curvature so that the resulting thrust variation is as limited as possible. A solution of this type, however, suffers from the size of the springs, which penalizes the compactness of the trolley design and requires greater spacing of the loads from the rail, which thus must be placed in a higher position. To obviate at least partially the problem, there have been used linkages and transmissions added to the bucking system or springs with several concentric stages with an increase in complexity and hence cost of the trolley, introducing also greater probability of breakdown.
Thrust means for the bucking wheels having substantially constant operation have the further disadvantage of supplying the same friction necessary for rising travel even during travel on horizontal sections where the weight of the trolley would be sufficient to ensure adherence of the drive wheel. This uselessly stresses the mechanical parts of the trolley and increases wear on the rolling members and the rail.
The general object of the present invention therefore is to obviate the drawbacks mentioned above by proving a conveyor system of the self-powered type which, while it can have trolleys of limited size and complexity, allow the use of ascending and descending ramps with relatively steep slopes without additional movement means and without introducing disadvantages for level travel.